1. Field of the Invention
This invention relates to the construction of drills, and particularly to drills which are specially adapted for drilling masonry, stone, rock, concrete, cement, cinder block, and the like.
2. Description of the Prior Art
Masonry drills have been known and are commonly used for drilling holes in especially hard friable material such as masonry or stone. These drills are usually comprised of an elongated body or shank having a spiral groove or grooves formed along their length and having a diametrically extending straight groove on their leading end. A hard insert was provided in the straight groove and was held in place by soldering or brazing. The insert usually had sharp cutting edges on its leading end so that the drill might effectively be used in the hard masonry or stone material. The spiral groove provided a channel for the discharge of chips, particles, dust and other drilling debris loosened by the leading end of the drill during the drilling operation. The insert must be capable of resisting wear, fracture, and the abrasive action of the chips from the material being drilled, while the body of the drill must maintain sufficient strength in the presence of heat generated in use.
In the manufacture of prior art masonry drills, it has been the practice to make the drill body of a material such as steel and to mount the abrasion-resistant insert or cutting elements at the cutting end. The body of the drill was normally formed by conventional rolling, machining or grinding the spiral thread in a blank or rod of suitable length. The straight groove for the mounting of the insert or cutting element was then machined in the leading end of the drill body, and the cutting element was placed and secured. The cutting element was formed of a hard material such as tungsten carbide and was usually anchored in place in the body of the drill by soldering or brazing it in place.
Examples of prior art masonry drills are shown in the following U.S. Pat. Nos.: 2,879,036 issued to Wheeler; 2,902,260 issued to Tilden; 3,372,763 issued to Fischer; 3,447,616 issued to Granat; 3,469,643 issued to Horst; 3,674,101 issued to Chromy; and 3,845,829 issued to Schaumann.
The manufacture of prior art masonry drills by these known processes has been relatively expensive. The initial expense of these masonry drills may be offset somewhat in industrial use by resharpening the hardened insert or cutting element a number of times. While satisfactory but expensive industrial quality masonry drills have been manufactured by this process, it has not been possible to provide inexpensive yet high quality masonry drills for nonindustrial users. The initial expense of a masonry drill provided to consumers through retail outlets such as hardware stores may not be offset by resharpening, since the average nonindustrial user generally does not have the capability of resharpening carbide tips. In addition, the tools purchased by nonindustrial users are often purchased for very limited use, such as to drill several holes needed for a particular job, and the drill may not be used again thereafter since the user may not have occasion to do so.
An additional cost associated with the manufacture of masonry drills of the prior art was the cost of inserting and soldering or brazing the cutting element or insert in place. Since it is important that the insert be firmly anchored in the drill body, there did not appear to be any means for eliminating this step in the manufacturing process.
There is presently a need for an inexpensive tool that will perform substantially equivalent to the conventional masonry drill yet will cost significantly less. The usable life of the body of such a drill need only be as long as that of the carbide tip, since the tip would probably not be resharpened. However, it is possible that such a drill may be resharpened, so that it would be advantageous if the body would outlast the tip.
It may be possible to reduce the cost of manufacturing with conventional methods, but this may require a major expenditure and an assurance of high volume production. Even with conventional methods, moreover, the cost reductions would not be significant.